In the Copenhagen Climate Conference in 2009, on year-on-year basis in 2005, the Chinese government promises that carbon emission will be reduced by 40-50% in 2020, which is a daunting task for us. Biological aviation kerosene is an oil product, prepared by using animal and vegetable oil as raw materials through a hydrogenated technology, having similar components as those of petroleum-based aviation kerosene. Main components are C8-C16 straight-chain and branch alkanes. Development of the biological aviation kerosene may reduce carbon emission. The biological aviation kerosene is renewable resource and may serve as an alternative fuel of petroleum. Therefore, the biological aviation kerosene has great significance. Castor serves as a plant with wide planting area and easiness in growth and is a crop suitable for oil production, and the prepared castor oil is not edible, i.e., the castor oil cannot be eaten by people. Therefore, the castor oil is an excellent renewable resource. The castor oil serves as a raw material, and high-yield aviation kerosene may be obtained by virtue of a hydrodeoxygenation process and a researched and developed catalyst, thereby alleviating energy crisis.
Stability of the catalyst is the most important in a hydrodeoxygenation reaction. Due to specific hydroxyl groups in the castor oil, a dehydration amount in the reaction is 2-3 times that of general grease, and thus the catalyst is required to have excellent hydrothermal stability. The large-specific surface nano-alumina designed in the present invention has excellent hydrothermal stability, and dispersion of active components may be increased due to a nano-structure of the alumina, thereby decreasing carbon deposit in the reaction and increasing the life of the catalyst. In a hydroisomerization reaction, the raw material is a product produced by utilizing the hydrodeoxygenation in the first step after dehydration, 90% of the components are C17-C15 alkanes, and 10% of the components are C5-C6 alkanes. Selectivity of carbon chains in the product is of vital importance, and the components of the aviation kerosene are required as C8-C16, so regulation of isomerizing and cracking degrees is very critical. Firstly, for a NiSAPO-11 carrier of a hierarchical pore channel, due to addition of Ni and a structure of the hierarchical pore channel, acid strength of a molecular sieve may be regulated in a controllable mode, thereby regulating the cracking degree of the isomerization reaction. Finally, the components of the aviation kerosene with the highest selectivity may be obtained. In addition, due to the adding of the carbon nano tubes, the strength of a catalyst carrier is well enhanced, and the catalyst carrier has active sites in the carbon nano tubes, so that a composite carrier has rich pore channels for isomerizing long-chain n-alkanes and decreasing the carbon deposit in the reaction, thereby increasing the life of the catalyst.
A preparation method for preparing hydrodeoxygenation and hydroisomerization catalysts of biological aviation kerosene with castor oil is disclosed in a patent CN201510038506.6. Titanium-modified and citric acid-modified MCM-41 are mainly used as a carrier of the hydrodeoxygenation catalyst. An active component selected by the hydroisomerization catalyst is Pt, Pd or Ni. A catalyst for preparing biodiesel through castor oil hydrogenation and a preparation method of the catalyst are disclosed in a patent CN201410020108.7. The carrier needs to be specially pretreated in the hydrodeoxygenation catalyst and the hydroisomerization catalyst. The carrier is pretreated by adopting an aqueous solution of acetic acid, and Zn serves as an assistant. A method for preparing biological aviation fuel by utilizing Litsea cubeba kernel oil is disclosed in a patent CN102719317A. and comprises the steps: carrying out a hydrodeoxygenation reaction and a hydroisomerization reaction on refined Litsea cubeba oil, distilling the obtained product to take a fraction between 150° C. and 280° C., and refining the fraction by using a fiber liquid membrane-composite adsorption combined apparatus and a dielectric field refining apparatus, thereby obtaining the biological aviation kerosene satisfying the usage conditions.
The above disclosed patents focus on hydrodeoxygenation activity and yield of the oil product, while the present invention prolongs the life of the catalyst by a designed catalyst with a specific structure while increasing activity and yield, so that the modified catalyst is more favorable for industrial production.